The present invention relates to a thermosensitive recording material, and more particularly to the improvement of a thermosensitive recording material comprising a support material and a thermosensitive coloring layer formed thereon, containing a colorless or light-colored leuco dye and a color developer capable of inducing color formation in the leuco dye upon application of heat thereto through a thermal reaction.
Conventional thermosensitive recording materials are provided with a thermosensitive coloring layer of which the main components are thermosensitive coloring components, on a support material such as paper, synthetic paper, or a plastic film, so that colored images are obtained by application of heat through a thermal head, thermal pen, laser beam, stroboscopic lamp, and the like. With this type of recording material, the recording can be obtained in a short time as compared with other recording materials, by using a comparatively simple device without the need for complicated processes such as developing and fixing. In addition to the above advantages, because of the advantages of low cost and small amount of noise and environmental pollution, this material has wide-scale utilization, not only as recording materials for copying books and documents, but also as recording materials for use with computers, facsimile machines, ticket vendors, recorders, and the like, and as recording labels.
In recent years, thermosensitive recording materials have gained further widespread application as recording materials in parallel with the progress in, in particular, the systemization of product systems and point of sale (POS) systems for product data and sales control.
The thermal color developing components used in this type of thermosensitive recording material usually comprise a coloring agent and a color developer capable of inducing color formation in the coloring agent upon application of heat thereto. Conventionally, as such coloring agents, leuco dyes having, for example, lactone, lactam, or spiropyran rings, are employed, and as such color developers, organic acids and phenolic acid materials are employed.
However, this type of recording material does not demonstrate satisfactory light resistance in image areas and the background, specifically because of the reduction in image density and the extreme discoloration of the background upon long-term exposure to fluorescent light or sunlight, especially in the application of labels in the systemization of POS. Conventionally, the addition of an ultraviolet-ray-absorbing compound, such as benzophenone, benzotriazole and salicylate, to the thermosensitive coloring layer, is commonly known as a method of improving the resistance to light. However, to simply include these ultraviolet-ray-absorbing compounds in the thermosensitive coloring layer gives rise to such a problem as fogging formation, due to an inadequate effect of absorption of ultraviolet rays, so that satisfactory results are not obtained.